That is down right false. There are platforms that use X11 and use EGL (for example N9, N900, Maemo, MeeGo, etc). Ubuntu on Tegra is X11 with EGL. These same platforms do NOT have glx.

Though in all honesty, EGL really does not buy you anything; it just means different startup kludge code to create a GL context, etc. The specification is more focused on GLES1/2/3 than desktop GL. Indeed, although EGL has a mechanism to create a GL context, it lacks all of the goodies found in wgl/glxCreateContexAttribsARB.

There is also Mesa EGL/ES2 on X11 Ubuntu 12.04, that I've seen in action.
Which seems handy for cross-developing for Android, etc.
Just recently I noticed that freeglut now supports EGL/ES2 as an alternative to GLX or WGL.

GLX is very X11 specific, so transitioning towards EGL brings significant benefits. I don't see why someone couldn't create a GLX over EGL wrapper, to help run legacy code on platforms without GLX. The main reason why EGL has become necessary, is to disconnect X11 from OpenGL. So it opens a multitude of use cases for OpenGL, or at least vastly simplifies their implantation..... To put this another way, EGL is no pulseaudio.